Adhesion and plastic surface treatment

The Adhesion problem is common in materials that possess low surface energies. Examples can include High-Density Polyethylene, Polypropylene, EPDM, and Polyethylene etc. With the surface energy ranging anywhere from twenty nine to thirty six Dyne/cm or mN/m (milinewton per meter). Surface treatment of plastic products

Obtaining a level of adhesion on any materials with low surface energy i.e. Polypropylene or Polyethylene etc. can sometimes become extremely difficult because of their slickness. Thus, this adhesion problem leads to the printed ink rubbing off, coatings or paint not sticking on the surface along with failed gluing and weak sealing.

Read the main article here: Dealing with the Adhesion Problem in Plastic Surface Treatment

Factors Leading to Improved Adhesion on Plastics

People working in the plastic coating industry are well aware of the problems pertaining to proper adhesion. Due to its excessively smooth surface, paints or coats do not adhere to the surface unless it’s treated. Untreated plastic surfaces contain low levels of surface energy which leads to poor bond formation with the adhesive. Improved adhesion on plastics results from the increased bonding strength that essentially depends on the liquid and substrates chemical nature.
Adhesion of material surfaces to coats, inks and paints etc. largely depends on the wettability of a particular surface. Wettability is known as a ratio of surface energy that exists between the substrate and liquid. Improved wettability would mean that a material is more likely to accept the changes made on its surface unlike the unresponsiveness shown through certain chemicals. Consequently, an adhesion problem will only occur if the wetted material has a surface energy level (measured in Dyne) that’s lower than that of the liquid.

The following methods can be used to obtain improved adhesion on plastics:

Promoted Adhesion

For improved adhesion, promoters like coating compositions, primers and tie-coats are largely used. That’s because these promoters use forces of attraction for bonding, bond covalently, and have chemical similarities that encourage adhesion.

In order to support adhesion, the promoter has to search for the functionality of a chemical existing within the plastic that’s ready for binding or bonding together with the promoter. Residual functionality on a reasonable level available for binding in thermoset surfaces will increase the promoter’s performance. Although, polymers having no or low residual functionality can create a problem during adhesion promotion. However, there are a number of other ways for promoting adhesion on plastic surfaces.

Silanes are a very popular group of promoters that are available for particular combinations of coatings and plastics. Adhesion coating can be difficult on substrates made from hydrocarbon thermoplastics and polyolefins. Therefore, promoters like polychlorinated polyolefin are used along with these substrates to help the coating bind with the plastic surface on chemical similarity.  Moreover, they have a propensity to migrate to the interface of the substrate due to their relatively hydrophobic nature.

Surface Treatment for Better Adhesion

Surface Treatment for Better Adhesion

Almost each and every surface open to the elements existing in the ordinary atmosphere goes through water and gas absorption within the molecular bounds. Oxidation processes can also bring about a change in surface conditions. Since exposure leads to the gathering of contaminants on a surface, it is imperative that the surface be treated prior to any kind of adhesion.

The quality of adhesion on a surface depends on the amount of surface energy a material possesses. If the surface energy is low, then the adhesion of coatings or inks is most likely to be unsuccessful. Coating, printing, painting etc. can be done on almost all kinds of surfaces.

But some materials require surface treatment or pretreatment before any actual coating takes place. Surface treatment modifies the surface of a material making it more adherent to the changes that are about to take place. Therefore, solving the adhesion problem becomes quite crucial.

Surface modification is carried out mostly on materials that are too expensive or sensitive for chemical or mechanical treatments. For example, wet chemical techniques create a lot of hassle when it comes to the treatment of surfaces. As many solutions and acids are used in this process to remove the foreign contaminants residing on the surface, the process ends with chemical residue covering the surface.

Hence, another round of cleaning is to be initiated for removing the residue of chemicals that were set to clean that surface in the first place. Other methods or pretreatment include pickling and sandblasting etc. which leave the surfaces more damaged than clean.